Reducing Tornado Fatalities
Outside Traditional “Tornado
Alley”
Erin A. Thead
May 2016
Introduction
Atmospheric scientists have long suspected that climate change produces an increase in weather
extremes of all varieties, but tornadoes are an unusually tricky case. A recent publication from the
National Academy of Sciences summarizes the state of the art in the new discipline of event
attribution, finding that that, although tornadoes are among the most difficult extreme weather
events attribute to anthropogenic climate change, improvements in modeling and climate-weather
model coupling have made possible some degree of probabilistic attribution.1 At present it seems
likely that the influence of climate change on tornadoes is indirect, manifested largely by more direct
influences on natural climate cycles such as the amplitude of waves in the jet stream that bounds the
polar vortex and the El Niño-Southern Oscillation (ENSO), with which severe tornado seasons and
their predominant locations have been loosely linked.2,3 Researchers are not yet in a position to say
for sure what if any role climate change has played in the increases in tornado frequency and severity
we have seen over the past 50 years.4
However, we need not wait until these issues are sorted out to begin working to protect vulnerable
populations. In what follows, I first give some background on the increasingly significant threat
posed by tornadoes and then outline some proactive steps governments and other entities can take
to keep people safe.
A Disturbing Trend
A disturbing trend has already developed concerning tornado fatalities. After several decades of
decline that can largely be credited to a great increase in forecasting skills and warning lead time, the
United States fatality rate for tornadoes has leveled off, although there may have been a slight
increase in recent years. Figure 1 shows United States tornado fatalities since 1940; Figure 2 shows
the trend line for 1985-2015. The figures also show linear (black) and nonlinear (red) trend lines
together with R2 values (the higher the number, the better the fit to the underlying data). As the
charts indicate, the long-term trend is a decrease, but in more recent years, the statistical trend is for
a slight increase, as is made clear by the better fit of the nonlinear curve to the 1940-2015 data.
Further statistical analysis of the 1985-2015 data shows that the statistical uptick is caused by the
outlier year of 2011. Removing this data point causes the trend lines for 1985-2015 to become flat.
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(There has also been a “tornado drought” from 2012-2015, with each year being below the
climatological average in total annual tornado count.) However, even if 2011 is considered an outlier,
it is evident that tornado fatalities in the United States are no longer in a decline.
Tornado Fatalities, 1940-2015
600
500
400
300
R² = 0.0778
200
R² = 0.1298
100
0
1930
1940
1950
1960
1970
1980
1990
-100
Figure 1
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2000
2010
2020
Tornado Fatalities, 1985-2015
600
500
400
R² = 0.0579
300
R² = 0.0619
200
100
0
1980
1985
1990
1995
2000
2005
2010
2015
2020
-100
Figure 2
The NOAA Storm Prediction Center has also tracked the circumstances of tornado fatalities since
2008. What tornado fatality data from 2008 to 2015 makes clear is that fatalities occur in markedly
different locations in violent (EF4 and EF5) tornadoes than in less intense tornadoes. This data pool
includes the modern-era record year of 2011. Although that year was a statistical outlier, it still
provides a large sample to examine the factors that now lead to tornado deaths in the United States,
particularly in the Southeast, Midwest, and Atlantic states—areas that do not fall into the traditional
designation of “tornado alley.”
Figure 3 shows 2008-2015 fatality circumstance information for EF0-EF3 tornado deaths, taken
directly from the Storm Prediction Center.5 Figure 4 shows this information for EF4 and EF5
tornadoes. The first graph demonstrates what decades of education and awareness have taught us,
namely, that mobile homes account for a disproportionately high death rate in weaker (relatively
speaking—EF3 tornadoes have up to 165 mph winds) tornadoes compared to their frequency of
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usage as dwellings. The second graph indicates a very different pattern. Almost any type of
residential structure can be leveled by violent tornadoes. A clear majority of deaths in violent
tornadoes occur in anchored buildings, whether residential or commercial.
EF0-EF3 Tornado Deaths,
2008-2015
0%
2%
5%
10%
Permanent House
26%
Mobile Home
Other Building
Outside
Vehicle
57%
Unknown
Figure 3
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Violent (EF4-EF5) Tornado Deaths,
2008-2015
11%
Permanent House
Mobile Home
8%
2%
44%
Other Building
Outside
17%
Vehicle
Unknown
18%
Figure 4
Dangerous Amateur Videography
One interesting point is that the percentage of deaths in vehicles and outdoors is similar between
EF0-EF3 and EF4-EF5 tornadoes. (The “unknown” category of fatalities may include even more
vehicular deaths.) This is an indication that it is dangerous to be in a vehicle or outside in any
tornado, a fact that has been known for years. However, there is a specific activity associated with
unprotected locations like these that is becoming more common: dangerous amateur videography. It
has only become a societal trend since the era of social media began, so it is not completely clear yet
what effect it is having on tornado injuries or fatalities. However, there is ample cause for concern.
Thousands of tornado videos are online, and many of them were not taken by experienced storm
chasers or security cameras—or by people who were a safe distance away. Tornado videos from
Tuscaloosa, AL (April 27, 2011) and Rochelle, IL (April 9, 2015) were shot by people who drove
into outer vortices and had car accidents while taking the video. A quick search of YouTube or
other video websites will easily uncover many more such dangerously filmed videos, most of them
with tens of thousands of views.
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Although there are some irresponsible storm chasers, over the past decade there has been awareness
in the storm chasing community of irresponsible behavior and group censure of it when it occurs.
Respected storm chasers do not condone dangerous video filming, especially by amateurs. This
particular trend was generated by social media culture, similarly to the trend of taking “selfies” in
various hazardous conditions (which has definitely resulted in fatalities6). Responsible storm chasers
and weather spotters make on-site reports, raising awareness and providing information about
storms. On the other hand, many people who happen to see a tornado now decide at once to get
video of it, and the videographers often are unaware of how far away they should be or where to go
if the tornado shifts its path. The people filming these videos sometimes say this in the footage, in
fact. Amateurs cannot be prevented from shooting videos in dangerous conditions, but newscasters
should not air them, as it implicitly encourages the behavior.
Urban and Suburban Storm Shelter Options
This, however, is a comparatively easy way to reduce tornado fatalities. A much more difficult one
involves storm shelters for buildings, and it is difficult both because of cost and geographical scope.
One ugly lesson forced on us in 2011 is that, contrary to long-standing cultural myths about
tornadoes mostly hitting rural trailer parks and prairie farmsteads, cities can be hit too, and the safety
options for urbanites are arguably more limited. Even in the age of high-resolution radar, real-time
reports, live coverage, and long lead times for warnings, we now know that an EF5 tornado striking
a moderately sized town can result in a triple-digit death toll, as happened in Joplin, MO. It is easy,
in retrospect, to understand why a densely packed urban area may be the worst possible place to be.
Other than the very center of high-rise office buildings, there is no safe place above ground. Highrises, according to the EF-scale, will not be demolished even in an EF5; the maximum expected
damage is “significant structural deformation.”7 However, directing everyone to the nearest tall
office building is completely infeasible, needless to say.
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In medium-sized urban areas like Joplin, many buildings in the central business district, such as
restaurants and small offices, are not constructed to withstand a tornado. Big-box retailers will
contain very heavy stock that is piled high, creating potentially deadly missiles and collapses.
Vehicles fill the roads and parking facilities. There is no easy way to get out of danger; traffic
congestion will occur if people try to evacuate en masse, possibly putting people in even greater
danger than they would have been if they had stayed put. And, of course, cities will generate more
debris than any other type of community. The volume of debris in Joplin was unprecedented.
Communal tornado shelters, which some smaller communities do have, would be useful in cities
only if people flocked to these sites well in advance, because congestion on the roads could result in
mass fatalities. Indeed, this very situation almost unfolded in Oklahoma on May 31, 2013, when a
newscaster urged people to “get out”—and they did.8 Major highways became “parking lots,” and
professional meteorologists estimated that the fatality count for the tornado could have been in the
hundreds if it had passed directly over these congested roads.9 Traditional storm cellars are all but
nonexistent in cities, and basements are directly beneath the houses, which puts anyone taking
shelter therein at risk of exposure to tornadic winds and suction if the house is removed.
Nonetheless, being in a basement is better than being above ground, so their construction should be
promoted in cities where they are uncommon in homes. Furthermore, a basement can be made very
safe by installing an engineered safe room.
It is rare for cities to be struck by violent tornadoes, but it can happen. The only reason why most
cities in tornado-prone areas do not get struck is that they do not occupy much land space. With an
increase in urban sprawl, this is changing. When cities are hit, the buildings do not provide frictionbased wind resistance that would mitigate violent winds; in fact, wind engineering analyses have
shown that a wind-tunnel effect actually occurs, which may increase the wind speed to which
residents will be subjected. The best suggestion for urban environments consists of promoting
structure designs and retrofits that offer increased resilience to natural phenomena.
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Violent tornadoes, those rated EF4 and EF5, will utterly demolish well-built houses, leaving only a
pile of debris over a foundation (EF4) or a bare foundation altogether (EF5). This fact readily
accounts for the high percentage of fatalities in anchored buildings, as shown in Figure 4.
Unfortunately, a majority of houses in the South and Midwest do not have basements or storm
cellars. Storm cellars are generally preferable to basements, unless a basement contains an engineered
safe room. There are enough accounts of people who took shelter in open basements and were
pulled out (e.g., the Parkersville, IA EF5 tornado of 200810, as well as several of the 27 April 2011
tornadoes) that open basements cannot be equated with storm cellars or basements with safe rooms.
Storm cellars where the entrance is not directly above the main room, but is horizontally removed
from it by a small underground passage, are even better. Firmly anchored handrails in the main
room are also advised, in case the door is torn away. This event has been documented in damage
photographs of EF5 tornadoes, including the Hackleburg tornado of 27 April 2011.11
Above-ground safe rooms are another shelter option that is less than ideal. These structures are
engineered, but they are vulnerable on two counts. First, they must be designed so that they will not
be undermined from below and will withstand the brunt of horizontal winds without breaking loose
of their anchorings. Considering that EF5 tornadoes can rip masonry walls from foundations even
when the walls are anchor-bolted, this is a tall order. Second, the engineering is based on impacts
from a flying missile the size of a two-by-four with a speed of 100 mph. EF5 tornadoes have wind
speeds upwards of 200 mph and have even been clocked as high as 300 mph. In Jarrell, TX, in 1997,
a slow-moving F5 tornado tragically destroyed an entire subdivision, including obliterating one
house with stone walls two feet thick.
Most tornadoes are not EF4 or EF5, and it is better, of course, to have an engineered safe room
than not, even an above-ground one. However, these shelters are safest when constructed in a
basement. Even FEMA documents concerning safe rooms acknowledge that “the likelihood of
wind-borne debris entering the basement is lower than for above-ground spaces” and that “repairs
to the walls, ceilings, and door of a safe room may be necessary after an extreme-wind event.” 12, 13
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The engineering analysis assumed that 100 mph is a typical projectile velocity in a tornado with wind
speeds of 250 mph, but even if that is the case in a real scenario, the size of the tested projectile is
not an upper bound on what is possible. In Smithville, MS, the town’s water tower was dented 120
feet above ground by an SUV that became airborne.14 In EF5 tornadoes in El Reno, OK in 2011
and Moore, OK in 2013, large metal tanks for oil and water storage were hurled over a mile from
their original sites. Video exists of a Canadian F5 tornado in which a whole house is airborne at a
great height before it disintegrates. There is, in short, a good reason why the National Weather
Service has for decades advised people to go underground in tornadoes.
Conclusion
It’s easy to say that everyone should have an underground shelter. It is much more difficult to make
it reality. This must be a matter of personal responsibility rather than a mandate on individuals,
which would be difficult to pass given political gridlock. The decision to install a storm shelter
probably needs to be rewarded with a tax rebate or credit. Such credits have been offered in the
past, usually to specific regions after particularly high-profile and destructive weather events; to
encourage their adoption, they should be permanent and universal. Disaster preparedness should be
encouraged before any disaster has ever struck, instead of being limited to communities that have
already been affected.
These are just a few suggestions about what types of measures might be taken to reduce tornado
fatalities and reverse the beginnings of the unwanted trend we are now starting to observe.
Undoubtedly others will focus on other possibilities, but one thing is certain: as the climate
continues to change, communities will find themselves at greater and greater risk from extreme
weather. It is best to make preparations now.
Erin A. Thead is a Graduate Research Fellow at the Climate Institute.
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Notes
1. National Academy of Sciences (2016). Attribution of Extreme Weather Events in the Context of Climate
Change. Washington, DC: The National Academies Press.
http://www.nap.edu/catalog/21852/attribution-of-extreme-weather-events-in-the-context-ofclimate-change
2. Cook, A. R., and J. T. Schaefer (2007). The Relation of El Niño–Southern Oscillation (ENSO)
to Winter Tornado Outbreaks. Monthly Weather Review, vol. 136, pp. 3121-3137.
http://www.spc.noaa.gov/publications/cook/enso-mwr.pdf
3. Masato, Giacomo, Brian J. Hoskins, and Tim Woollings (2013). Winter and Summer Northern
Hemisphere Blocking in CMIP5 Models. Journal of Climate, vol. 26, pp. 7044-7059. September
2013. http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00466.1
4. Tippett, Michael, and Joel E. Cohen (2016). Tornado outbreak variability follows Taylor’s power
law of fluctuation scaling and increases dramatically with severity. Nature Communications, vol. 7,
article no. 10668
http://www.nature.com/ncomms/2016/160229/ncomms10668/abs/ncomms10668.html
5. Cook, A. R., and J. T. Schaefer (2007). The Relation of El Niño–Southern Oscillation (ENSO)
to Winter Tornado Outbreaks. Monthly Weather Review, vol. 136, pp. 3121-3137.
http://www.spc.noaa.gov/publications/cook/enso-mwr.pdf[4
6. NOAA Storm Prediction Center (2016). Annual U. S. Killer Tornado Statistics.
http://www.spc.noaa.gov/climo/torn/fataltorn.html
7. CBS News (2016). Death by Selfie. http://www.cbsnews.com/news/death-by-selfie/
8. NOAA Storm Prediction Center (2007). Enhanced F Scale for Tornado Damage.
http://www.spc.noaa.gov/efscale/ef-scale.html
9. Samenow, Jason (2013). The day that should change storm chasing forever. Washington Post.
https://www.washingtonpost.com/news/capital-weather-gang/wp/2013/06/01/the-night-thatshould-change-tornado-actions-and-storm-chasing-forever/
10. Masters, Jeff (2013). A Night of Tornado Chaos in Oklahoma City.
http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2422
11. National Weather Service Des Moines, IA. Parkersburg-New Hartford, Iowa EF-5 Tornado.
http://www.crh.noaa.gov/Image/dmx/parkersburg/Final-small-PDF-PARKERSBURGNEW-HARTFORD-IOWA-EF-5-TORNADO.pdf
12. Examining the Phil Campbell Tornado – The Ultimate EF5 (2012). ExtremePlanet.
http://extremeplanet.me/2012/09/01/examining-the-phil-campbell-tornado-the-ultimate-ef5/
13. FEMA (2014). Taking Shelter from the Storm. http://www.fema.gov/media-librarydata/1418837471752-920f09bb8187ee15436712a3e82ce709/FEMA_P-320_2014_508.pdf
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14. FEMA (2003). Residential Safe Rooms. http://www.fema.gov/media-library-data/201307261529-20490-1894/resshelter_bkgrdr.pdf
15. National Weather Service Southern Region Headquarters (2011). Smithville, Mississippi EF5
Tornado Damage.
http://www.srh.noaa.gov/srh/srnews/stories/2011/outbreak_smithvilleEF5.htm
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